So: why complain that I'm slow to finish, but not want to do things she has previously said were fun that work better for me?
Why wear sexy lingerie around the house, but not want sex?
How can BJs be OK on my birthday, but absolutely disgusting and abusive at other times?
Why claim to, and appear to greatly enjoy sex, but always find excuses not to do so?
(and no, she won't answer these questions, or answers with a specific reason for a specific thing, not the general answer)
Short answer - it's a control thing for her. Maybe completely subconsciously. She WANTS you to want her, but often, that's enough for her. BJ's are 'abusive', but not on your birthday, because it's her choice to do so. She'll wear enticing lingerie frequently, but it doesn't mean she's in the mood - she wants you to pay her some attention.
My wife is similar in many respects (and not just about sex). She DOES want me to want her, but it's almost as though that's all she wants.
A good example - a few weekends ago, I did not pursue sex with her on our scheduled/unscheduled day (ie the day sex is normally expected by both of us). I was tired, and not particularly in the mood, so I snuggled up with her in bed that night, and eventually fell asleep. The next morning, she woke me up to have sex. This never happens. I'd like to say that nonsexual intimacy the night before got her in the mood (and perhaps it did) but I know my wife quite well. This was more for her self esteem, IMO. I didn't pursue her the night before, and that doesn't sit well with her. This is not the first time I've either declined or otherwise 'rejected' her, and every time it's happened, it bothers her.
In other words, she reserves the right to decline or otherwise not be interested, but I'm not afforded the same courtesy. In other OTHER words, she wants to be in control.
When your wife wears lingerie around the house, she's expecting you to be interested, and as such, she can decline your advances when she pleases (which seems to be often). For many, simply being desired is the goal, and the physical interactions are unnecessary for their mental and emotional state. Again, I see this in my wife. Although the physical is enjoyed by her, it's not the ultimate goal. When I don't pay attention to her, she notices. I don't believe she's completely conscious of this, either.